The present invention relates broadly to a helicopter radar system and in particular to a helicopter discrimination apparatus having the capability to discriminate between missiles and assorted clutter.
The murine radar is a helicopter-borne system which is designed to detect infrared-seeking interceptor missiles, and launch a flare in time to decoy the missile away from the helicopter. In order to separate the missile's radar return from that of the ground doppler filtering is employed. This is possible because the doppler shift which is produced by an approaching missile is higher than any doppler component that is received from the ground. However, the tip velocity of the helicopter rotor blade is within the range of velocities which are achieved by an intercepter missile and thus signals from nearby helicopters may have doppler frequency components which are high enough to cause false radar alarms. Since the operation of helicopters in the vicinity of or in formation with other helicopters is a common tactical requirement, it is important that these false radar alarms be minimized or eliminated. Characteristics of radar signals from helicopter rotor blades have been studied both in the time domain and in the doppler frequency domain. It has been observed that a characteristic of the rotor blade time signatures after doppler filtering is its very short duration during each revolution of the rotor blade. This time duration is typically 5 msec with a period of 83 msec. The present invention provides an apparatus which rejects non-missile related doppler signals and thus prevents false alarms.